Solar-reactive mulch film

Abstract

A solar reactive mulch film comprising one or more layers of heat shrink material pre-strained at a predetermined temperature and tension. Immediately cooling the pre-strained layers retains molecular deformation stresses in the material which facilitate shrinkage but not expansion on exposure to solar radiation. The mulch film adapted to be laid over longitudinal growing beds and held tautly by burying its side edges in soil. Exposure of uncovered portions of film to solar radiation causes shrinkage in one or more directions whereby in combination with the weight of the soil holding it down, maintains tautness of the mulch over a growing period. Methods of manufacture and use of the same.

What is claimed is: 
     
       1. A solar-reactive agricultural mulch film comprising:
 a sheet of heat-shrink material including one or more layers of linear low density polyethylene (LLDPE) and/or metalocene linear low density polyethylene (mLLDPE), wherein one or more of the layers of LLDPE and/or mLLDPE having dispersed, in a polyethylene consisting essentially of LLDPE and/or mLLDPE, carbon black particles, in an amount that ranges between 2% and 8% by weight, that absorb radiant energy from sunlight and convert the radiant energy to heat, such that a surface temperature of the sheet is raised to at least a shrinking temperature of 40° C., which is above an ambient surface temperature of the sheet but not above a melting point of one or more of the layers of LLDPE and/or mLLDPE; and wherein, when one or more of the layers of LLDPE and/or mLLDPE is less than the shrinking temperature, each of one or more of the layers of LLDPE and/or mLLDPE is elongated, in a lengthwise direction, beyond a yield point of each of one or more of the layers of LLDPE and/or mLLDPE such that main chain molecules of the LLDPE and/or mLLDPE and/or side branched molecules of the LLDPE and/or mLLDPE in each of one or more of the layers of LLDPE and/or mLLDPE are aligned and elongated in the lengthwise direction and resultant plastic deformation stresses, resulting from elongation beyond the yield point, are retained and each of one or more of the layers of LLDPE and/or mLLDPE does not shrink. 
 
     
     
       2. The solar-reactive agricultural mulch film of  claim 1 , wherein the sheet of heat shrink material comprises:
 a single-wound plastic sheet; or 
 a bonded and blocked double-wound plastic sheet forming a single resulting sheet. 
 
     
     
       3. The solar-reactive agricultural mulch film of  claim 1 , wherein the film further comprises at least one additive selected from the group consisting of:
 a process aid; 
 an anti-oxidization additive; 
 an ultraviolet light stabilizer; 
 an ultraviolet light absorber; 
 a plasticizer; and 
 a lubricant. 
 
     
     
       4. The solar-reactive agricultural mulch film of  claim 3 , wherein the ultraviolet light stabilizer comprises a hindered-amine light stabilizer (HALS). 
     
     
       5. The solar-reactive agricultural mulch film of  claim 1 , wherein the sheet of heat-shrink material comprises two or more co-extruded layers of LLDPE and/or mLLDPE. 
     
     
       6. The solar-reactive agricultural mulch film of  claim 1 , wherein a one or more of the layers of LLDPE and/or mLLDPE is impermeable to gas. 
     
     
       7. The solar-reactive agricultural mulch film of  claim 1 , wherein one or more of the layers of LLDPE and/or mLLDPE contains carbon black particles having a particle size that ranges between 17 and 100 nanometers. 
     
     
       8. The solar-reactive agricultural mulch film of  claim 1 , wherein the carbon black particles are provided in one or more of the layers of LLDPE and/or mLLDPE so that the sheet of heat-shrink material is black in color or opaque to ensure the sheet of heat-shrink material blocks light transmission and absorbs sufficient solar energy to heat the sheet of heat-shrink material sufficiently to initiate shrinkage. 
     
     
       9. The solar-reactive agricultural mulch film of  claim 1 , wherein the carbon black particles are present in an amount between 4% and 7% by weight of at least one of the layers of LLDPE and/or mLLDPE and have a particle size that ranges between 17 and 50 nanometers in size. 
     
     
       10. The solar-reactive agricultural mulch film of  claim 1 , wherein the carbon black particles are present in an amount between 5.6% and 6.4% by weight of at least one of the layers of LLDPE and/or mLLDPE and have a particle size that ranges between 17 and 21 nanometers in size. 
     
     
       11. The solar-reactive agricultural mulch film of  claim 1 , wherein an upper surface of the solar-reactive agricultural mulch film is white. 
     
     
       12. The solar-reactive agricultural mulch film of  claim 1 , wherein the sheet of heat-shrink material has different colors on either surface. 
     
     
       13. The solar-reactive agricultural mulch film of  claim 1 , wherein one or more of the layers of LLDPE and/or mLLDPE shrinks at least 25% in the lengthwise direction once the surface temperature of the sheet of heat-shrink material reaches 40° C. 
     
     
       14. The solar-reactive agricultural mulch film of  claim 1 , wherein the heat-shrink material comprises the mLLDPE. 
     
     
       15. The solar-reactive agricultural mulch film of  claim 1 , wherein the heat-shrink material has a uniform thickness. 
     
     
       16. The solar-reactive agricultural mulch film of  claim 1 , wherein, during an operational state of the solar-reactive agricultural mulch film, when the shrinking temperature of the sheet of the heat-shrink material reaches or exceeds the shrinking temperature, the sheet of heat-shrink material shrinks substantially in the lengthwise direction such that at least a portion of the main chain molecules of the LLDPE and/or the mLLDPE and/or the side branched molecules of the LLDPE and/or the mLLDPE are not aligned in the lengthwise direction to reduce the deformation stresses of the sheet of heat-shrink material. 
     
     
       17. The solar-reactive agricultural mulch film of  claim 1 , wherein, during an operational state of the solar-reactive agricultural mulch film, the sheet of heat shrink material is placed adjacent to a surface of a growing bed and when the shrinking temperature of the sheet of the heat-shrink material reaches or exceeds the shrinking temperature, the sheet of heat-shrink material shrinks such that the sheet of heat-shrink material tightens against the surface of the growing bed, and does not expand.